[New Page] Median U-turn intersection

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[New Page] Median U-turn intersection

Postby kentsmith9 » Wed Mar 19, 2014 7:04 am

A rather lengthy discussion has been taking place in the Michigan forums on documenting the "Michigan Left Turn." To be more universal the group has proposed the name be redefined as "Median U-Turn Intersection."

They have been working on a proposal for the wiki here.

I propose that we get some initial feedback on the page as it stands and then create a full page for it with the additional changes we might come up with here.

If someone from the original team wants to lead the general Wiki page creation, that is fine, or I can do it if desired.
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Re: [New Page] Median U-turn intersection

Postby CBenson » Wed Mar 19, 2014 2:20 pm

I think this would make a good wiki page. Maryland has taken to implementing many Restricted Crossing U-Turn (RCUT) / Super-Street Median Crossover intersections and I do believe that the guidance for the U-turn roads should be similar. Currently the U-turn roads are typically not typed as ramps here (because it conflicts with the wiki so they get changed when they are made ramps). They also aren't typically configured to give the second turn left instruction. But if those in Michigan that have more experience with these types of U-turns have determined that the second instruction is helpful, I don't see an issue with including it on RCUT intersections as well.
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Re: [New Page] Median U-turn intersection

Postby kentsmith9 » Wed Mar 19, 2014 3:08 pm

CBenson wrote:I think this would make a good wiki page. Maryland has taken to implementing many Restricted Crossing U-Turn (RCUT) / Super-Street Median Crossover intersections and I do believe that the guidance for the U-turn roads should be similar.

Is there an RCUT page in development by anyone? I did not see "RCUT" in the Main or User namespaces, so I assume not.

CBenson wrote:Currently the U-turn roads are typically not typed as ramps here (because it conflicts with the wiki so they get changed when they are made ramps).

If we need a Ramp there for the right reasons, then we should update the Wiki. Do we need a separate thread just on Where to allow Ramps? I am not familiar with all these other intersection types on the Michigan page. In California we just put up lights and bring everything to its knees. :lol:
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Re: [New Page] Median U-turn intersection

Postby CBenson » Wed Mar 19, 2014 3:55 pm

kentsmith9 wrote:Is there an RCUT page in development by anyone? I did not see "RCUT" in the Main or User namespaces, so I assume not.

There isn't one that I'm aware of. They are mentioned on the page you referenced as a variant of the Median U-Turn Intersection. Essentially, they do not allow the straight movement of the secondary road through the intersection. Example here. Seems to me that the U-Turn roads should be treated similarly for the "MUTI" and the "RCUT," and thus the requirements for the U-Turn roads can be set forth in this one wiki page.

kentsmith9 wrote:If we need a Ramp there for the right reasons, then we should update the Wiki. Do we need a separate thread just on Where to allow Ramps?

I don't think we need a separate thread. These intersections are simply an exception to the guidance not to use ramps for at grade connectors.
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Re: [New Page] Median U-turn intersection

Postby sketch » Wed Mar 19, 2014 5:02 pm

Whether or not a second instruction is used should depend on the physical characteristics of the U turn. That's why we use a second instruction everywhere in Michigan but not everywhere in Louisiana.

  • Detroit area: yes second instruction. Traffic exits at an 80–90° angle.
  • New Orleans suburbs: no second instruction. Traffic exits at ~45° angle.
  • New Orleans: yes second instruction. Traffic exits at 90° angle.

The two things that will apply to every instance of an MUTI are the ramp type and the initial (turn left) instruction. The two things that will vary based on application will be the second instruction (above) and the naming. But they should vary differently, I believe:

  • Naming standards should be consistent within a state or at least within a metropolitan area. MUTIs in Detroit should be named like the ones in the suburbs even if Detroit does not sign its MUTIs as diligently as the suburbs do. MUTIs in New Orleans are signed "U turn" even though New Orleans doesn't typically sign U turns because every such U turn is signed as such in the suburbs (at least in Jefferson Parish, which comprises the bulk of New Orleans's suburbs). People driving throughout the area will expect the same type of instruction throughout.
  • Geometry standards for the exit node should be set according to the geometry of the U turn segment itself, but typically a particular locality will have its own standards for their construction. It's a factual determination — if every such segment in an area/state is designed the same way, set a standard for the area/state; otherwise, set standards per municipality, whether published or de facto, or simply set the geometry per-intersection or per-road.

As far as I'm concerned an RCUT is a type of MUTI.

Louisiana has installed a bunch of RCUTs on US-90 in southwestern La.; they've taken to calling them "J turns".
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Re: [New Page] Median U-turn intersection

Postby kentsmith9 » Wed Mar 19, 2014 5:55 pm

CBenson wrote:These intersections are simply an exception to the guidance not to use ramps for at grade connectors.

I think wherever we say there is an exception, we need to describe why we would do it in one place and not another. For example the [[At-grade connectors]] page says why to use ramps there so people understand the reason. In the U-turn page we just need to do the same thing to explain the "why." Part of the process of teaching people to fish. :D
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Re: [New Page] Median U-turn intersection

Postby sketch » Wed Mar 19, 2014 6:09 pm

Are you saying this exception should be described and explained briefly (incl. the justification for it) on the at-grade connectors page, but explained in detail on its own page? I'd agree.

Jughandles should be handled similarly, unless it is decided that they don't merit their own page; then we could just redirect "Jughandle(s)" to the AGC page. But this can be discussed with its own thread or in the general AGC page thread that's active right now.
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Re: [New Page] Median U-turn intersection

Postby CBenson » Wed Mar 19, 2014 6:23 pm

kentsmith9 wrote:I think wherever we say there is an exception, we need to describe why we would do it in one place and not another. For example the [[At-grade connectors]] page says why to use ramps there so people understand the reason. In the U-turn page we just need to do the same thing to explain the "why." Part of the process of teaching people to fish. :D

Doesn't the U-turn page do that with the following:
Road Type: RAMP
Although this departs from traditional rules for at-grade connectors and for use of the ramp road type, it hides the instructional street name in the client. It is close to the exception stated on the at-grade connector page, however, in that a MUTI is a signed--though unnumbered--exit from the current direction of travel on a roadway.

Otherwise, you get other workarounds like this segment.
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Re: [New Page] Median U-turn intersection

Postby kentsmith9 » Thu Mar 20, 2014 3:30 am

CBenson wrote:
kentsmith9 wrote:I think wherever we say there is an exception, we need to describe why we would do it in one place and not another. For example the [[At-grade connectors]] page says why to use ramps there so people understand the reason. In the U-turn page we just need to do the same thing to explain the "why." Part of the process of teaching people to fish. :D

Doesn't the U-turn page do that with the following:
Road Type: RAMP
Although this departs from traditional rules for at-grade connectors and for use of the ramp road type, it hides the instructional street name in the client. It is close to the exception stated on the at-grade connector page, however, in that a MUTI is a signed--though unnumbered--exit from the current direction of travel on a roadway.

Otherwise, you get other workarounds like this segment.

I was only speaking generically that we need to explain why we have any exceptions for any rule. That current explanation on the U-turn page seems to be covering most of it. I know we currently only get the Exit instruction for Right turns and we have asked for it to be controllable or also added to Left turns, but that was part of the reason for the exception for At-grade connectors. I don't assume that was the reason for ramps on the U-turn page (which I just now realized). Therefore it seems to cover the exception reason nicely.
sketch wrote:Are you saying this exception should be described and explained briefly (incl. the justification for it) on the at-grade connectors page, but explained in detail on its own page? I'd agree.

Jughandles should be handled similarly, unless it is decided that they don't merit their own page; then we could just redirect "Jughandle(s)" to the AGC page. But this can be discussed with its own thread or in the general AGC page thread that's active right now.

I would agree with all of the above. :D
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Re: [New Page] Median U-turn intersection

Postby qwaletee » Thu Mar 20, 2014 7:40 pm

Perhaps reference and/or crib form http://www.fhwa.dot.gov/publications/re ... ety/09059/

Note that it gives an alternative name of J-turn, which may be more approachable for lay editors.
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